The invention relates to a process for producing coarse-grained sintered magnesia, starting from a pulverulent magnesium oxide, converting this into green compacts and subjecting the green compacts to sinterfiring at high temperature.
To obtain the desired high-temperature strength in sintered magnesia products, it is necessary to achieve a sufficiently high density of the sintered magnesia, which is usually abbreviated to "sinter". As a rule, an apparent density of the sintered magnesia of 3.3 g/cm.sup.3 is regarded as a minimum value, but the aim is to reach apparent densities above 3.4 g/cm.sup.3. In order to meet this aim, the green compacts which are to be subjected to the sintering treatment at high temperature, at which deadburning of the material takes place, must already have a sufficiently high density of at least about 1.7 g/cm.sup.3, but preferably more than 2.3 g/cm.sup.3, and a structure which tends to give considerable compaction on mild firing. To form such green compacts, magnesium oxide has hitherto been compacted by means of mechanical presses, so-called briquetting roller presses having in particular been used for this compaction. However, the use of mechanical presses for the formation of green compacts of a density which meets the abovementioned demands, requires a relatively large investment expense and, in operation, the consumption of considerable quantities of energy, because very high forces must be applied for compacting the pulverulent magnesium oxide. In spite of the application of high forces, however, a relatively large proportion of the green compacts provided by the presses has an unduly low mechanical strength. Such green compacts disintegrate during the manipulation which follows pressing and, for reprocessing the material which was contained in these green compacts, this material must be screened off and subjected to repeated pressing, which results in a considerable increase in the energy consumption required for pressing and a corresponding decrease in the production output of the presses, since, in fact, a considerable part of the magnesium oxide to be processed must be compacted several times.